1. Field of the Invention
The present invention relates to papermakers fabrics for supporting and conveying fibrous webs, and more particularly to a papermakers fabric formed from a plurality of individual links joined by pintles in an interconnected array to form an endless belt.
2. Description of the Prior Art
In papermaking machines, a papermakers fabric in the form of an endless, belt-like structure is supported on and advanced by various rolls on a papermaking machine during the papermaking process. Papermakers fabrics carry various names depending upon the portion of the machine in which they are used. By way of example, such fabrics can include forming fabrics, wet press felts, and dryer felts and fabrics, to name just a few.
Forming fabrics, also sometimes known as fourdrinier wires, or forming media, are utilized at the "wet end" of the papermaking process, where a water-fiber slurry is deposited thereon, and are commonly made from a length of woven fabric having its ends joined together in a seam to provide an endless belt. Such a fabric can also be formed by employing an endless weave process, thereby eliminating the seam. Either construction generally comprises a plurality of machine direction yarns and a plurality of cross machine direction yarns which have been woven together on a suitable loom to form a foraminous web of interwoven yarns having a predetermined permeability.
Recently, synthetic fibers have been used in the papermaking field, in whole or in part, to produce forming fabrics of superior quality as compared with the materials formerly employed. The use of synthetic fibers has increased to the point that almost all forming fabrics now are made from polyesters, such as those sold under the trademarks Dacron or Trevina; from acrylic fibers, such as those sold under the trademarks Orlon, Dynel, and Acrylan; from copolymers, such as those sold under the trademark Saran; or from polyamides, such as those sold under the trademark Nylon. The machine direction and cross machine direction yarns of the forming fabric can be of the same or of different materials or constructions, and they can be in the form of either a monofilament or a multifilament yarn.
Among the problems prominent in conventional, woven forming fabrics are edge curling and the need to control fabric permeability without adversely affecting fabric strength and stability. Additionally, the repair of distorted, torn, or otherwise damaged fabrics is both costly and time consuming, and because of the woven nature of the various papermakers fabrics, there is no easy way to repair them and oftentimes they must be replaced in their entirety.
A conventional dryer felt, which is used at the dry end of the papermaking machine, consists of an endless belt made from a two- or three-ply fabric wherein the various plies are defined by different groups of cross machine direction yarns. The plies are united into a unitary structure by a plurality of machine direction yarns. The yarns used to weave the most up-to-date dryer felts are made from monofilaments or multifilaments, and from such synthetic materials as polyesters or polyamides.
Because synthetic fibers are quite expensive, manufacturers are continually seeking to provide improved dryer felts, both in terms of lower cost and in terms of extended dryer felt reliability. Along these lines, it is important in certain dryer felts to maintain low liquid permeability, and one way of lowering the permeability is to weave more yarn to the inch. This, of course, adds further to the cost of such already expensive felts.
Many of the prior art woven papermakers fabrics employ seams by which the ends of the fabric are joined together through the use of a rod-like member called a "pintle" in order to facilitate insertion and removal of the fabric from the papermaking machine. A very common type of seam is one employing metal clipper hooks arranged in an alternating relationship on either end of the fabric belt, which serve to receive a pintle therebetween when the hooks are brought into interengaging relationship and thereby join the ends of the belt together.
In some papermakers fabrics, the ends of the fabrics are joined in an abutting relationship and held that way through the use of clipper hooks inserted in a webbing, the whole of which is attached to the underside of the fabric. Such an arrangement causes an undesirable seam mark in the paper sheet. Another problem with such seamed fabrics is bouncing of the fabric, which occurs when the seam of the fabric either makes or leaves contact with a machine roll. This bouncing causes further marking of the paper sheet and, in an extreme case, it could cause paper sheet breaks, as well as rapid weakening of the fabric structure in the seam area.
There is thus a need for a papermakers fabric which functions reliably in the various environments encountered in the course of the papermaking process, and which can be produced inexpensively and efficiently. It also is desirable that the papermakers fabric be endless in construction and easily repaired while in position on a papermaking machine. It is an object of the present invention to overcome the above-described shortcomings of existing papermakers fabric structures.